title: Reproducibility of interfraction lung motion probability distribution function using dynamic MRI: statistical analysis.
abstract: OBJECTIVE
  To investigate the statistical reproducibility of craniocaudal probability distribution function (PDF) of interfraction lung motion using dynamic magnetic resonance imaging.
  
  
  METHODS
  A total of 17 subjects, 9 healthy volunteers and 8 lung tumor patients, underwent two to three continuous 300-s magnetic resonance imaging scans in the sagittal plane, repeated 2 weeks apart. Three pulmonary vessels from different lung regions (upper, middle, and lower) in the healthy subjects and lung tumor patients were selected for tracking, and the displacement PDF reproducibility was evaluated as a function of scan time and frame rate.
  
  
  RESULTS
  For both healthy subjects and patients, the PDF reproducibility improved with increased scan time and converged to an equilibrium state during the 300-s scan. The PDF reproducibility at 300 s (mean, 0.86; range, 0.70-0.96) were significantly (p < 0.001) increased compared with those at 5 s (mean, 0.65; range, 0.25-0.79). PDF reproducibility showed less sensitivity to imaging frame rates that were >2 frames/s.
  
  
  CONCLUSIONS
  A statistically significant improvement in PDF reproducibility was observed with a prolonged scan time among the 17 participants. The confirmation of PDF reproducibility over times much shorter than stereotactic body radiotherapy delivery duration is a vital part of the initial validation process of probability-based treatment planning for stereotactic body radiotherapy for lung cancer.
authors.affiliation: Department of Radiation Oncology, University of Virginia, Charlottesville, VA 22908, USA.
authors.forename: Jing
authors.initials: J
authors.lastname: Cai
authors.forename: Paul W
authors.initials: PW
authors.lastname: Read
authors.forename: James M
authors.initials: JM
authors.lastname: Larner
authors.forename: David R
authors.initials: DR
authors.lastname: Jones
authors.forename: Stanley H
authors.initials: SH
authors.lastname: Benedict
authors.forename: Ke
authors.initials: K
authors.lastname: Sheng
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D016477:Artifacts; D003627:Data Interpretation, Statistical; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009038:Motion; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D015656:Respiratory Mechanics; D012680:Sensitivity and Specificity; D016008:Statistical Distributions